1. Field of the Invention
The present invention relates to improvements in depolarizers and improvements in circular dichroism (CD) spectrometers in terms of accuracy.
2. Description of the Related Art
Circular dichroism (CD) spectrometry has been widely used as virtually the only spectroscopic method for analyzing the three-dimensional structures of molecules directly. The method was initially used to determine absolute structures of bioactive natural organic compounds and in the stereochemical study of complex compounds, and was subsequently used in biochemistry to analyze the high-order structures of biological polymers such as proteins. The method has been very useful to measure the thermal stability of biological polymers and to analyze the reaction processes of enzyme reactions, for example. In the pharmacology and pharmaceutical industry, the method has been indispensable to reduce side effects by analyzing molecular asymmetry and medical effects and to control the activity of enzymes incorporated in drugs and the like.
CD spectrometers are broadly divided into ECD spectrometers for measuring primarily circular dichroism related to electron transitions in the ultraviolet, visible, or near-infrared region and VCD spectrometers for measuring primarily circular dichroism related to vibrational transitions in the infrared region. Since a spectrum obtained by measurement is close to a spectrum predicted in calculation from a molecular structure, the application of VCD spectrometers is expanding to the structural analysis of drugs and biologically active substances.
In a conventional CD spectrometer, a polarizer transmits only light having a specific linear polarization included in a light beam coming from a light source; a photoelastic modulator modulates the linearly polarized light alternately into a right-handed circularly polarized light beam and a left-handed circularly polarized light beam; and the right-handed and left-handed circularly polarized light beams are alternately directed onto a sample. Because of the difference in absorbance of right-handed and left-handed circularly polarized light beams in the sample due to the properties of the sample, the intensity of light transmitted through the sample depends on the right-handed or left-handed rotating of circularly polarized light. A detector detects the intensity of light transmitted through the sample, and signal processing means calculates the difference in absorbance between the right-handed and left-handed circularly polarized light beams, that is, circular dichroism on the basis of variations in the light intensity signal of the transmitted light. Through that process, the internal structure and other properties of the sample are investigated.